U.S. patent number 4,976,377 [Application Number 07/234,869] was granted by the patent office on 1990-12-11 for liquid and powder measuring apparatus.
This patent grant is currently assigned to Fuji Photo Film Co., Ltd.. Invention is credited to Noboru Higuchi, Yasunori Ichikawa, Chuzo Kobayashi, Keizo Matsui, Shigeru Yamaguchi.
United States Patent |
4,976,377 |
Higuchi , et al. |
* December 11, 1990 |
Liquid and powder measuring apparatus
Abstract
A liquid or powder measurement apparatus, usable also for mixing
a plurality of measured materials and for distributing the mixture
to a plurality of dispensing containers. A flow control valve
having a wide flow rate range and excellent linearity between the
degree of valve opening and flow rate is disposed in each of the
liquid flow paths and is adjustable to have a flow rate linearly
varying with the stroke of the valve. A mixing container receives
the raw material from one or more supply containers and is weighed
by a load cell to thereby detect the amount of material flowing
into or out of the mixing container. A control unit operating
according to fuzzy logic compares the measured weight with a target
weight and accordingly adjusts the flow rate of a selected one of
the flow regulators. The same load cell and control unit can also
control the flows from the mixing containers to the dispensing
containers.
Inventors: |
Higuchi; Noboru (Kanagawa,
JP), Kobayashi; Chuzo (Kanagawa, JP),
Ichikawa; Yasunori (Kanagawa, JP), Matsui; Keizo
(Kanagawa, JP), Yamaguchi; Shigeru (Kanagawa,
JP) |
Assignee: |
Fuji Photo Film Co., Ltd.
(Kanagawa, JP)
|
[*] Notice: |
The portion of the term of this patent
subsequent to May 16, 2006 has been disclaimed. |
Family
ID: |
27529408 |
Appl.
No.: |
07/234,869 |
Filed: |
August 22, 1988 |
Foreign Application Priority Data
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Aug 21, 1987 [JP] |
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62-206587 |
Aug 21, 1987 [JP] |
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62-206588 |
Oct 1, 1987 [JP] |
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62-245755 |
Oct 1, 1987 [JP] |
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62-245757 |
Oct 14, 1987 [JP] |
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62-257393 |
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Current U.S.
Class: |
222/55;
137/487.5; 222/129; 222/56; 222/63; 251/122; 706/900 |
Current CPC
Class: |
G01F
1/76 (20130101); G01G 13/285 (20130101); G01G
17/06 (20130101); G05D 11/132 (20130101); Y10S
706/90 (20130101); Y10T 137/7761 (20150401) |
Current International
Class: |
G01F
1/76 (20060101); G01G 13/285 (20060101); G01G
17/00 (20060101); G01G 13/00 (20060101); G01G
17/06 (20060101); G05D 11/13 (20060101); G05D
11/00 (20060101); B67O 005/08 () |
Field of
Search: |
;222/55,56,59,63,14-17,20,129 ;251/210,122 ;137/403,486,487.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0290889 |
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Apr 1988 |
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EP |
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158270 |
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Jan 1983 |
|
DE |
|
Other References
Zadeh, L. A., "Outline of A New Approach to the Analysis of Complex
Systems and Decision Processes", IEEE Transactions, vol. SMC-3, No.
1, pp. 28-44. .
Mamdani, E. H., "Application of Fuzzy Algorithms for Control of
Simple Dynamic Plant", Proceedings, IEE, vol. 121, No. 12 (Dec.
1974), pp. 1585-1588..
|
Primary Examiner: Skaggs; H. Grant
Assistant Examiner: Reiss; Steven
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Claims
What is claimed is:
1. A closed loop measuring apparatus, comprising:
a supply tank containing a stock material;
a motor;
a flow regulating valve attached to an outlet of said tank and
having a linear stroke controlled by an operation of said motor,
said valve providing a flow rate therethrough of said stock
material which is substantially linear with said stroke and which
is finely controlled over an entire range of flow rates between a
closed position of said valve to a fully open position;
a detector for measuring a quantity of said stock material
transferred through said valve; and
a control unit receiving an output of said detector and a
measurement target value and controlling said motor in a successive
closed loop operation cycle.
2. A closed loop measuring apparatus as recited in claim 1, wherein
said control unit operates according to fuzzy inference upon said
measured quantity and said measurement target value.
3. A closed loop measuring apparatus as recited in claim 2, wherein
said stock material is a liquid and said valve is a liquid
valve.
4. A closed loop measuring apparatus as recited in claim 1, further
comprising:
a plurality of said supply tanks storing respective stock
materials;
a plurality of said motors;
a plurality of said flow regulating valves controlled by respective
ones of said motors and providing a flow rate therethrough of a
respective one of said stock materials which is substantially
linear with said stroke of a respective one of said valves; and
a measuring tank receiving said stock materials flowing through
said valves and having said detector attached thereto;
wherein said control unit controls each of said motors.
5. A closed loop measuring apparatus, comprising:
a supply tank containing a stock material;
a motor;
a flow regulating valve attached to an outlet of said tank and
having a linear stroke controlled by an operation of said motor,
said valve providing a flow rate therethrough of said stock
material which is substantially linear with said stroke;
a detector for measuring a quantity of said stock material
transferred through said valve;
a control unit receiving an output of said detector and a
measurement target value and controlling said motor in a successive
closed loop operation cycle, wherein said control unit operates
according to fuzzy inference upon said measured quantity and said
measurement target value;
wherein said stock material is a liquid and said valve is a liquid
valve;
wherein said motor has a feed screw; and
wherein said valve comprises:
a valve casing having a central axis and comprising an inlet side
casing and an outlet side casing;
a valve head with a circular truncated-cone shaped working face for
engagement with said valve casing a portion between said inlet and
outlet side casings and a tapered portion extending from said
working face in a direction of said outlet side casing and having a
cross section tapering away from said working face, said tapered
portion being disposed within said outlet side casing in a fully
closed position of said valve and within said inlet side casing in
a fully open position of said valve; and
a valve shaft attached to said valve head and extending along said
central axis;
and wherein said apparatus further comprises:
a linearly guided coupling board on which is mounted said valve
shaft and is moved by said feed screw, whereby said coupling board
and said valve shaft move as a unit.
6. A closed loop measuring apparatus as recited in claim 5, wherein
said outlet side casing is substantially circular and wherein an
area of said cross section of said tapered portion of said valve
head decreases substantially linearly with a distance along said
central axis from said working face.
7. A closed loop measuring apparatus as recited in claim 6, wherein
said tapered portin is cone shaped.
8. A closed loop measuring apparatus comprising:
a supply tank containing a stock material;
a motor;
a flow regulating valve attached to an outlet of said tank and
having a linear stroke controlled by an operation of said motor,
said valve providing a flow rate therethrough of said stock
material which is substantially linear with said stroke;
a detector for measuring a quantity of said stock material
transferred through said valve; and
a control unit receiving an output of said detector and a
measurement target value and controlling said motor in a successive
closed loop operation cycle;
further comprising:
a plurality of said supply tanks storing respective stock
materials;
a plurality of said motors;
a plurality of said flow regulating valves controlled by respective
ones of said motors and providing a flow rate therethrough of a
respective one of said stock materials which is substantially
linear with said stroke of a respective one of said valves; and
a measuring tank receiving said stock materials flowing through
said valves and having said detector attached thereto;
wherein said control unit controls each of said motors;
wherein each of said motors has a rotary output shaft;
wherein each of said valves comprises:
a valve casing having a central axis and comprising an inlet side
casing and an outlet side casing;
a valve head with a circular truncated-cone shaped working face for
engagement with said valve casing in a portion between said inlet
and outlet side working face in a direction of said outlet side
casing and having a cross section tapering away from said working
face, said tapered portion being disposed within said outlet side
casing in a fully closed position of said valve and within said
inlet side casing in a fully open position of said valve; and
a valve shaft attached to said valve head and extending along said
central axis;
and wherein said apparatus for each of said motors and each of said
valves further comprises:
a linearly guided coupling board on which is mounted said valve
shaft and is moved by said output shaft, whereby said coupling
board and said valve shaft move as a unit.
9. A closed loop measuring, mixing and distributing apparatus,
comprising:
a plurality of supply containers containing respective raw
materials;
a mixing container for receiving and mixing said raw materials from
said supply containers to form a mixture;
a plurality of dispensing containers receiving said mixture from
said mixing container;
a plurality of flow regulators disposed in respective flow paths
between said supply containers and said mixing container and in
respective flow paths between said mixing container and said
dispensing containers, each of said flow regulators providing a
plurality of non-zero flow rates of material therethrough:
a detector associated with said mixing container for detecting an
amount of flow of material into and out of said mixing
container:
a control unit receiving an output of said detector and responsive
to target values associated with each of said flow regulators for
controlling an opening degree of each of said flow regulators
according to fuzzy inference: and
a switching unit for switching an output of said control unit to a
selected one of said flow regulators.
10. An apparatus as recited in claim 9, wherein each of said flow
regulators has a dead zone in which no material flows therethrough
within a range of operation of an operable part of said each flow
regulator.
11. An apparatus as recited in claim 9, further comprising means
for moving said mixing container between different ones of said
flow paths.
Description
FIELD OF THE INVENTION
This invention relates to a liquid and powder measuring method and
associated apparatus. It more particularly relates to a liquid and
powder measuring method in which control, such as fuzzy inference,
is carried out according to observation data obtained during the
measurement, and the flow speed of a liquid or powder to be
measured is gradually changed thereby to improve the measurement
accuracy, to increase the range of measurement, and to realize a
short measurement time.
The present invention also relates to a liquid measured mixing
apparatus for mixing various kinds of raw-material liquids after
metering to prepare a new mixture liquid.
The present invention relates to an apparatus for measured mixing
and distributing liquids for respectively measuring and mixing
various kinds of raw-material liquids to prepare a mixed liquid and
for metrically distributing the mixture liquid to a plurality of
tanks.
The present invention also relates to a liquid/powder
metering-mixing-dispensing system for measuring various kinds of
respective liquids and powders as raw materials, mixing these raw
materials to newly prepare a mixed material, and dispensing the
mixed liquid to dispensing containers. More particularly, the
present invention relates to a liquid/powder
measuring-mixing-dispensing system for measuring a wide flow rate
change of liquids and powders as raw materials, mixing these raw
materials and dispensing the mixture precisely and efficiently.
DESCRIPTION OF THE BACKGROUND
For the measurement of liquids, various detection methods such as a
weight type detection method (load cells). pressure type detection
method (differential pressure transmitters) and volume type
detection method (oval flow meters) have been employed. For
measurement of powders a weight type detection method using a load
cell has been mainly employed.
In any one of the detection methods, it is an essential premise for
measurement control that the flow speed is constant. A closed loop
measurement control method in which the flow speed is continuously
varied has not yet been proposed in the art.
In order to improve the measurement accuracy, the following methods
have been employed.
In a first method, the flow speed in a flow control valve is
changed in two steps so that, when the measurement target value is
approached, the flow speed is switched over to a slow flow speed
(c.f. Japanese Patent Application (OPI) No. 148019/1981). In a
second method, an amount of inflow (or amount of head) is set as a
measurement stopping condition, and the amount is predicted to
suspend the measurement (c.f. Japanese Patent Application (OPI) No.
29114/1982). (The term "OPI" as used herein means an unexamined
published application.)
In the conventional measurement control the flow speed is constant
or it is switched in two steps as was described above. However, in
a certain range, the measurement is carried out with the flow rate
fixed. Therefore, the conventional measurement control suffers from
the following disadvantages.
The first disadvantage is the measurement accuracy. The measurement
accuracy may not be guaranteed because of the variation of flow
speed which is caused by disturbance or by the variation of
physical characteristic (such as viscosity) of the liquid.
For instance in the conveyance of a liquid by gravity, the residual
amount of liquid to be measured remaining in the upstream container
(referred to a "a head difference" in this specification) affects
the flow speed of the liquid. If the head difference changes
greatly, then the flow speed goes out of a certain range, thus
adversely affecting the measurement accuracy. As a result, the head
of the upstream container must be limited to remain in a narrow
variation range. Therefore, in order to maintain the head
difference in a predetermined range, it is necessary to suspend the
measurement or to supply a suitable amount of raw material to the
upstream container, with a secondary loss of raw material.
The second disadvantage is the measurement range. Since the flow
speed is limited, the ratio of the minimum measurement value to the
maximum measurement value is of the order of 1:5.
In the case where the flow speed is switched in two steps the ratio
is of the order of 1:10 at maximum.
The reason why the measurement range must be narrow, as described
above is as follows. Even if the measurement is suspended, some
amount of liquid flows in because of the delay in response of the
system. The amount of inflow is determined by the flow speed.
Therefore in the case where the measurement target value is small,
the amount of inflow exceeds the accuracy-guaranteed limit. As a
result, the measurement range is limited.
In a plant which manufactures a variety of solutions, for one and
the same raw material a measurement range of about 1:100 at maximum
is available, and it is necessary to select a measuring apparatus
in a range of measurement target values.
The third disadvantage is the measurement time. The measurement
time depends on the measurement target value.
When the measuring target value is small, the measurement time is
short: and when large, the measurement time is long.
When the measurement target value is small, the operation time of
the system fluctuates and the measurement accuracy cannot be
guaranteed, with the result that the measurement range is
decreased.
In a system of mixing a plurality of measured solutions to prepare
a new solution, the manufacturing capacity depends on the
measurement time. Especially in a pipeless movement type
manufacturing system, the conveying capacity is limited.
The above-described difficulties result in economical disadvantage
in the formation of the production line. That is, heretofore, a
number of liquid and powder measuring apparatus are installed
according to measurement target values. Such a measuring apparatus
is provided for each optimal measurement time determined from the
limitation of manufacturing capacity, or for each raw material to
be handled. That is, a large number of measuring apparatuses are
installed.
Recently, one of the present applicants has developed and filed a
patent application on the following technique in order to provide a
liquid and powder measuring method in which the above-described
difficulties are eliminated. The measurement is carried out with
high accuracy being free from the variation of flow speed due to
disturbances and the variations of liquid physical characteristics
(such as viscosity) and of powder physical characteristics (such as
fluidity). A wide range of measurement is established and a short
time measurement is realized independent from the measurement
target value.
That is, Japanese Patent Application No. 106412/1987 discloses a
closed loop liquid measuring method in which a freely determined
measurement target value and a fed back actual measurement value
are utilized to change the flow speed. In this methods the flow
characteristic of an opening degree control valve for controlling
the flow rate of a liquid and a measurement target value are
utilized for fuzzy inference to determine an initial valve opening
degree prior to the measurement. The fuzzy control of the valve is
carried out according to actual measurement values obtained
successively to change the valve opening degree.
Furthermore, Japanese Patent Application No. 106413/1987 discloses
a closed loop measurement control method in which a measurement
target value and fed back actual measurement value are utilized to
vary the flow speed. The difference between a measurement target
value and an actual measurement value output by a detector adapted
to measure a material to be measured and the variation (with time)
of the difference are utilized to apply an output to operating
means which varies the flow speed by fuzzy control, learning
control or optimal control, whereby the flow speed is optimized.
This application also discloses an apparatus for practicing the
method.
In the closed loop liquid and powder measurement control method in
which fuzzy control, learning control or optimal control of flow
control means is carried out, a fundamental factor which makes the
conventional measuring apparatus disadvantageous (i.e., the
condition that the flow speed is constant) is changed. That is, the
flow speed is changed by closed loop control. Therefore, a wide
range of measurements can be achieved in a short time without being
affected by the variation of flow speed due to disturbances and
independently of the measurement target values.
However, the method depends greatly on the flow control valve used.
That is, if the flow control valve is large in size, then
measurement of a small amount of liquid finally remaining takes a
relatively long time. On the other hand, if the flow control valve
is small in size, then it takes a long time to measure all the
liquid.
Heretofore, in order to make measurements more accurate, measuring
units have been used which are of the type which invariably limit
the flow rate of each liquid in the process of metrically mixing
and distributing the liquids.
In the prior art type of liquid measured mixing and distributing
apparatus, such measuring units must be respectively associated
with supply tanks from which liquids to be metrically mixed are
supplied to one tank.
In the case of using a volumetric type of measuring unit as shown
in FIG. 19 two measuring units must be provided with two loop
control functions for predictive flow rate control corresponding to
two types of supplied liquids.
A liquid regulating unit and liquid supply method are disclosed in
Japanese Patent Unexamined Publications Nos. 56-74715 (1981) and
58-163426 (1983). According to these publications, the flow rates
of liquids are measured by a common measuring unit but liquid
supply means for limiting the flow rate are controlled by
respectively independent control loops.
This is because, contrary to expectation, highly accurate
measurements cannot be attained by one and the same control
function since the flow rates of liquids vary according to the
quantities of liquids in the supply tanks, flow rate
characteristics of valves, physical properties of liquids, and the
like.
This applies to the case of measuring units of the tank metering
type, in which actuators of stop valves incorporated in respective
systems must be controlled by respective independent loop control
systems.
To attain a highly accurate measurement, a method has been proposed
in which valves having different flow rates are arranged in
parallel to each other so as to be switched based on predetermined
metering deviation. Also in this method, two loop control functions
are required.
The expression "two loop control functions" is used herein for the
following reason. In the case of using, for example, a distributed
control unit, two control units are not always required because
measuring can be made within one and the same control unit. It may
however be said that one control unit as viewed in terms of
hardware is separated into two control units as viewed in terms of
the number of inputs and outputs and software.
Further, the conventional liquid measured mixing apparatus and
measuring distribution apparatus are independent of each other
regardless of the measuring unit and control unit. Further, the
measuring precision in the prior art has been very rough because of
using a volumetric flow meter, ON/OFF control of valves, and the
like.
The conventional liquid measured mixing apparatus and measuring
distribution apparatus have the following disadvantages because the
metrical control is made on the assumption that the flow rate is
substantially constant.
A first problem in the conventional apparatus is the measuring
accuracy.
A change of flow velocity caused by disturbance or caused by a
change of liquid physical properties brings about a situation that
accuracy cannot be secured.
In the case of gravity transport, the flow velocity of an outflow
liquid always changes according to the residual quantity of liquid
within each supply tank. The flow velocity may exceed a certain
conditional limit if the change of the residual quantity is too
large, resulting in deterioration in accuracy.
To improve accuracy, the quantity of liquid within each supply tank
must be limited within a certain range to keep the quantity of
liquid above a predetermined value, resulting in liquid loss to
thereby increase running cost.
A second problem with the conventional apparatus is the measurement
range since the measuring range is narrow. This is because,
immediately after measuring stops, the inflow of liquid cannot stop
because of the delay of response of the system. Because the
quantity of the liquid inflow is determined by the flow velocity,
the allowable inflow quantity is secured by narrowing the measuring
range under the condition that the flow velocity is constant.
Accordingly, even in the case where two liquids to be measured are
quite the same, measuring units each having a proper measuring
range are required, resulting in an increase in number of the
units.
A third problem with the conventional apparatus is the measuring
time. Since the measuring time is affected by the measurement
target value. As the target value becomes smaller, the measuring
time becomes shorter, while as the target value becomes larger, the
measuring time becomes longer. Accordingly, measuring units suited
to the manufacturing cycle are required to correspond to the
measured value, resulting in an increase in the number of the units
if there are different target values.
Because a large number of independently controlled measuring units
are provided for respective supply tanks and distribution tanks and
for respective optimum measuring times due to the limitation of
manufacturing capacity for the aforementioned reason, the system of
the conventional liquid measured mixing and distributing apparatus
is complicated. In short, a large number of measuring units are
required corresponding to the number of distribution tanks
The present invention has been attained in view of such
circumstances, and an object of the present invention is to provide
a liquid measured mixing and distributing apparatus in which the
distribution system for liquids is constructed as a consecutive
system by use of a measuring control unit by which highly accurate
metering without influence of a change in flow velocity caused by
disturbance or cause by a change in liquid physical properties and
short-time metering to secure a wide metering range regardless of
the metering set values. Such a system can be attained on the basis
of a fuzzy-control liquid measured mixing apparatus described in
Japanese Patent Application No. 62 113430 (1987) previously filed
by one of the applicants of this application. Particularly a
measured mixing apparatus and a measuring distribution apparatus
are synthesized as one apparatus to thus attain an increase of
manufacturing capacity and a reduction of raw-material loss to
produce the following economic effects:
(1) A reduction of initial cost due to the reduction of the number
of units;
(2) A reduction of the frequency of maintenance due to the
reduction of the number of units;
(3) A reduction of breakdowns due to an improved reliability due to
the reduction in the number of units; and
(4) A reduction of running cost due to the reduction of
raw-material loss, and the like.
In measuring devices applicable to a conventional liquid/powder
measuring-mixing-dispensing system, the flow velocity has been set
as a constant and therefore accurate measurement has hardly been
attained thereby. In other words, the measuring device has been
designed to measure the flow velocity restricted to what
corresponds to a set measuring flow instead.
In the liquid/powder measuring-mixing-dispensing system of a
conventional type designed to mix the liquids or powders supplied
from a plurality of supply containers to one mixing container and
to dispense the mixed liquid to dispensing containers, each of the
supply containers and dispensing containers is equipped with a
measuring device attached thereto.
When volumetric metering devices are employed in a liquid/powder
measuring-mixing system, for instance, two measuring devices are,
as shown in FIG. 20 used respectively for two supply containers of
a liquid A and a powder B. Consequently, a control unit will be
required to have a double loop function in order to control the
quantity of a liquid or powder fluid preliminarily flowing into a
mixing container.
In other words, because the speed of the flowing liquid or powder
varies with the liquid or powder quantity in the supply container
of the liquid A or the powder B, the characteristics of the flow
rate regulator and the physical properties of the liquid or powder,
no accurate measurement can be expected from a single loop control
function.
This is also the case with a tank metering method in which a
shut-off valve of an actuator attached to each system has to be
controlled by an independently looped control system.
There is a method of installing parallel flow rate regulators with
different flow velocities, the regulators being switched with a
predetermined measuring variation to implement accurate
measurements. Even in this case, however, the double loop control
function is required.
The reason for the use of an expression of the double loop control
function above is that, though the data can be processed in one
control unit, provided a switch unit or the like is employed, for
instance, the necessity of more than one physical control unit can
be avoided. Notwithstanding, the system still relies on two
effective control units in view of the number of input/output
terminals and software.
In the batch production process in which a number of liquids or
powders are used, the physical properties of these liquids or
powders are different and this makes it often impossible to
cumulatively measure then in one and the same container.
Accordingly, a production system shown in FIG. 21 becomes
justified. This production system is arranged so that a plurality
of mixing containers (measuring hoppers and measuring-metering
tanks) are installed. Mixable liquids and powders are fed into and
measured in the same mixing container (measuring tank or hopper as
a first mixture), whereas liquids and powders unmixable with the
first mixture are accommodated in a separate container hopper or
tank). Another mixing container (control tank) for controlling the
reaction and preparation is required on the downstream side and
consequently the system tends to become complicated.
In a production system where a mixing container (control tank) for
controlling the reaction and preparation is fixed, a high initial
investment is required in facilities corresponding to the contents
of the products when many types are produced. Furthermore, to
implement accurate measuring, there are required a number of
measuring tanks and control tanks with piping, measuring devices,
control units and associated valves which are attached thereto. In
this case, the facilities are usable for some types of products but
unusable for others and therefore the system becomes highly
wasteful of facilities and also causes the initial facility cost to
increase. The introduction of a multipurpose production system is
being called for but such a production system tends to become
further complicated, because not only the piping system but also
the attachment devices will have to be altered if it is of a fixed
type (e.g., Japanese Patent Application (OPI) Nos. 74715/81,
155412/81, 72015/82 and 81559/79).
As a result, there has recently been proposed a moving batch
production system in which a mixing container (metering tanks,
control tanks) is movable. When the conventional metering devices
are applied to that system, however, the measuring time varies with
the size of a measurement target value and, if the target value is
large, it takes much time for the measurement and imposes a
restriction on the time required to convey the containers in the
moving production system. For this reason, the required number of
measuring devices is installed in the conventional production
system so as not to restrict the time of conveyance. However, this
arrangement is likely to conflict with the intended advantages of
the moving production system. Further, the length of stay at a
station tends to become prolonged in such a system. A large number
of measuring devices are required because of the range of
measurement target values, restrictions on the measuring time,
conditions of measuring precision, etc. Consequently, the time
required for the operation of the coupling pipes increases.
As photosensitive materials are dealt with in the process of
producing photographic materials, light must be shielded out and
the increased number of joints results in the complication of the
system, whereas the performance of the products is readily affected
by a change of the conveyance cycle.
Moreover, the measuring-dispenser of the mixed liquid does not
share the measurement control system with the measuring mixer.
Besides, the measuring device attached to each dispensing container
is employed to implement a simple open loop measuring control
method by means of a level gauge or time metering.
As measurement control presupposing a constant supply flow velocity
is performed in the conventional liquid/powder
measuring-mixing-dispensing system, the following drawbacks are
similar to those of the liquid measuring-mixing system.
(1) Measurement precision: Measurement precision is not always
ensured because of the fluctuation of flow velocity resulting from
disturbance and changes in the physical properties of the liquids
or powders.
More specifically, the selection of a conveyor depends on the
physical properties of the powder, e.g., a damper is used to convey
granular powder because it offers excellent fluidity, whereas a
screw feeder is used to convey powder whose fluidity is poor.
However, the flow of the powder cannot be precisely determined but
may be changed by the bulkiness or profile of the powder, and
disturbances such as vibration. When liquids or powders are
gravity-conveyed, the velocity of the flowing-out liquids or
powders varies with the residual amounts of the liquids or powders
in the supply container, for instance. However, if the residual
amount greatly varies, the measuring accuracy will deteriorate as
the flow velocity exceeds the set range of conditions.
This means that the quantity of the liquids or powders in the
supply container has to be limited to within a certain range so
that more than a fixed quantity of the liquids or powders is
secured in the container. Otherwise the lose resulting from the
residual liquids or powders in the supply container would increase
the running cost.
(2) Measuring range is narrow.
The reason for this is that there remains an inflow due to delay in
the response of the system to the suspension of measuring. In view
of this fact, the allowable inflow is ensured by narrowing the
measuring range on the condition that the flow velocity is constant
because the inflow is determined by the supply flow velocity.
Measuring devices respectively having adequate measuring ranges are
required when the set measurement target values greatly differ from
each other even if the same liquid or powder is to be measured.
Consequently, the number of measuring devices to be installed
increases.
(3) Measuring time: The measuring time is influenced by the set
measurement target value. The greater the set target value, the
shorter the measuring time becomes, and vice versa. Accordingly,
the measuring device has to offer proper measurement times in terms
of the production cycle in proportion to the set target value. The
number of measuring devices increases also in this case.
For the above-described reasons, a number of individually
controlled measuring devices are provided for the supply containers
respectively at optimum measurement intervals under the
restrictions of the production capacity in the conventional
liquid/powder measuring-mixing-dispensing system. Accordingly, the
system has become complicated in construction, whereas a large
number of measuring devices are required to be incorporated in the
production facilities. As a dispenser, the system is incapable of
high measuring precision, wasteful of liquid and also needs
prolonged time for the measurement.
SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to provide a liquid and
powder measuring method and apparatus in which a novel flow control
valve having excellent performance is used so that the measurement
be achieved with high accuracy in short time, and a wide range of
measurements can be accomplished being free from the variation of
flow speed due to disturbance. Furthermore, the apparatus is of
simple design.
The foregoing object of the invention has been achieved by the
provision of a closed loop liquid measuring method in which the
flow characteristic of a flow control valve for adjusting the flow
rate of a liquid and a freely determined measurement target value
are utilized for performing fuzzy inference, learning control or
optimal control to determine an initial valve opening degree prior
to the measurement. Fuzzy control of the flow control valve is
carried out according to actual measurement values which are
detected successively. According to the invention, the flow control
valve is a motor-controlled flow control valve which is small and
linear in the rate of change of flow rate with valve stroke and
large in the maximum flow rate.
In the fuzzy inference of the invention, the data directly observed
or calculated and the data directly observed or calculated and the
data subjected to low-pass filtering are used for control
processing operation with the dynamic characteristic of a measuring
detector taken into account.
In the control method, fuzzy control is employed, and with respect
to the membership function of the fuzzy inference the axis for
physical data is expressed semi-logarithmically.
The initial valve opening degree is determined by the fuzzy
inference which is made according to the flow characteristic of the
valve and the measuring set value. Then, the amount of operation is
calculated by the fuzzy control method and outputted to the
operating terminal.
In the method of the invention, the fuzzy control, learning control
or optimal control is non-linear in the modeling of the measuring
system, and therefore it cannot be realized by a control system
such as a conventional simple PID control system.
Therefore, according to the control method used in the invention,
the difference between a measurement target value and an actual
measurement value and the variation with time of the difference are
utilized to calculate an optimal amount of operation. The control
may be either fuzzy control, learning control or optimal control.
Thereby the flow speed is continuously or intermittently changed
best for the measurement control.
In the invention, the detector observes the variation with time of
the measurement value. It may be a load cell or a differential
pressure transmitter which can observe measurement values. In the
invention, the range of measurement depends on the static accuracy
of the detector.
In the invention, the measuring tanks for receiving liquid and
powder are such that the tanks receive liquid and powder,
respectively, or each tank receives both liquid and powder, as the
case may be. For simplification of the equipment, a method of using
one measuring tank to receive both liquid and powder may be
employed, if it does not adversely affect the product.
The above-described detector is fixedly or detachably coupled to
the measuring tank.
In the invention, the motor-controlled flow control valve which is
small and linear in the rate of change of flow rate with valve
stroke and large in the maximum flow rate is designed as follows.
An electric motor is used to operate the valve. The rotation of the
motor is converted into a linear motion by means of a feed screw
and a coupling board. The coupling board is connected to the valve
shaft, so that the coupling board and the valve shaft are moved as
one unit. The valve has a casing along the central axis of which
the valve shaft extends. The casing is made up of an upper end
portion, namely, an inlet-side casing, and a lower end portion,
namely, an outlet-side casing merging with the inlet-side casing. A
cylindrical or conical valve head is formed on a working face
shaped as a circular truncated cone, which is tapered towards the
outlet of the valve, in such a manner that the valve head is
positioned inside the outlet-side casing. The valve head is so
shaped that, with respect to the valve opening degree defined by
the surface of the valve head and the valve seat, the rate of
change of flow rate with valve stroke is small and linear, and the
valve stroke to fully open the valve is provided in the inlet-side
casing.
Although the foregoing object of the present invention was
generally solved by a previous invention proposed by the Applicant
of this application in Japanese Patent Application No. 62-110857.
The present invention which can provide further effects has been
attained as a result of research thereafter.
That is, the liquid measured mixing apparatus cumulatively measures
and mixes a plurality of liquids to prepare a mixture liquid by
closed-loop liquid metering method while a velocity of flow is
allowed to change. The apparatus according to the present invention
comprises a plurality of supply tanks respectively filled with
liquids as raw materials, a liquid receiving tank for mixing the
liquids received from the supply tanks, a plurality of flow control
valves respectively associated with the supply tanks a detector
arranged to the liquid receiving tank to metering the liquid, a
measurement control unit for performing fuzzy control on the basis
of actual values measured by the detector and arbitrarily set
target values so as to calculate the opening degrees of the
respective flow control valves, and a switching unit for switching
the output of the measurement control unit to a predetermined one
of the flow control valves. An electric motor is used as motive
power for adjusting at least one of the flow control valves. The
rotation of the electric motor is converted into a linear motion by
means of a feed screw and a connection plate. The at least one flow
control valve has a valve shaft attached to the coupling plate so
that the valve shaft moves vertically according to the vertical
motion of the coupling plate. An inlet-side valve box is arranged
around the valve shaft. An outlet-side valve box is connected to
the inlet-side valve box. A valve face is in the form of a tapered
circular truncated cone. A cylindrical or conical valve head is
mounted on the front of the valve face and installed within the
outlet-side valve box. A valve seat is arranged to form a valve
opening area between the valve seat and a surface of the valve
head. The shape of the valve head is determined so that the rate of
change in flow velocity is small and linear relative to a valve
lift which is kept within said inlet-side valve box till the
opening of said valve seat is completely opened.
The foregoing object of the present invention is further attained
by a liquid measured mixing and distribution apparatus in which
flow velocity can be changed from moment to moment by measurement
control units through closed-loop control so that the measurement
control units can be reduced in number. The liquid measuring mixing
and distribution apparatus of the present invention comprises the
following constituent parts.
(1) Supply tanks: Tanks for storing liquids to be measured. The
capacity of each tank is built on a scale suited to manufacturing.
In the present invention, there is no limitation as to the residual
quantity of liquid remaining in each tank. Theoretically, the
residual quantity of each tank can be measured down to zero. The
measurement of the residual quantity is not affected by the
physical properties (such as viscosity and the like) of liquid, so
that the residual quantity can be measured down to zero as long as
the liquid has a physical property allowing it to flow out.
(2) A mixer tank: A tank having capacity suited to the
manufacturing scale. The tank is provided with a stirrer for
mixing. The tank may have a jacket structure to make heat
insulation possible through the circulation of warm water. It is,
however, necessary to stozzzzzzz the circulation of warm water when
the weight of liquid is measured with a weight gauge. Further, the
measurement control unit must have such a function that the weight
can be automatically reset to apparent zero as a measurement start
point whenever weighing is started.
(3) Distribution tanks: A suitable number of tanks to which a mixed
liquid is distributed are arranged corresponding to the
manufacturing system.
(4) Flow-control valves: A suitable number of flow-control valves
each for varying the flow velocity by the change of the opening
degree thereof are provided corresponding to the number of supply
tanks and the number of distribution tanks. Each valve has such a
structure that the valve is closed at the opening degree in the
vicinity of 0%, while the valve is opened to pass liquid at the
opening degree in the vicinity of or over about 10%. When the
opening degree is over 10%, the valve has a variable flow-rate
characteristic other than a quick-open characteristic. The valve
may be actuated by a driving source, such as an AC servomotor or
the like.
(5) A detector: The detector is a device arranged on the mixer tank
for the double purpose of measuring the quantities of liquids
received by the mixer tank and measuring the quantities of liquids
distributed from the mixer tank. In the case where liquids can be
mixed, the liquids can be cumulatively measured through one and the
same liquid-receiving tank.
(6) A measurement control unit: This unit is an accurate
measurement control unit for performing closed-loop control to
change the flow velocity. The measurement and distribution of
respective liquids are made by one and the same measurement control
unit. The opening degree of each opening-regulated valve is made
variable by a control system according to fuzzy inference. That is,
the initial opening degree of the valve is determined by the
flow-rate characteristic target value of the valve. After the
initial opening, the opening degree of the valve is controlled
according to fuzzy inference based on the actual value and the
target value. When the control unit performs a function of additive
metering (a function of measuring liquids while receiving them),
the liquids from the supply tanks can be measured. When the control
unit provides a function of subtractive metering (a function of
measuring liquids while transporting them), the liquid can be
distributed to the downstream tanks in the proportion of suitable
quantities. A plurality of liquids can be measured by use of one
and the same tank and one and the same measuring unit to thereby
reduce the number of measuring units in number.
(7) A switching unit: A unit for switching the output of the
measurement control unit to suitable one or ones of the
opening-regulated valves in the liquid supply system and the mixed
liquid distribution system.
While the basic constituent parts of the present invention have
been described the subject of the present invention resides in that
a closed-loop measurement control unit is used to vary flow
velocity for performing control based on fuzzy inference.
An object of the present invention made in view of the aforesaid
disadvantages of conventional devices awaiting remedy is to provide
a liquid/powder measuring-mixing-dispensing system economically
having the effect of reducing:
(1) the initial cost by decreasing the number of measuring
devices;
(2) maintenance delays by decreasing the number of devices; and
(3) running cost by reducing the raw material loss.
The above objects are achieved by making use of a liquid
measuring-mixing apparatus under fuzzy control as applied by the
present applicants in Japanese Patent Application No. 115894/87.
This method provides precision measurements unaffected by flow
velocity fluctuations due to disturbances being measured. It
secures a wide range of measurements, and implements short time
measurements unaffected by the size of the set measurement target
value. It further forms the liquid/powder measuring
mixing-dispensing system into a consistent one in order to simplify
the production facilities and to augment the production capacity
while reducing the raw material loss.
The foregoing object of the present invention is accomplished by
providing a liquid/powder measuring-mixing-dispensing system for
cumulatively measuring liquids and powders supplied from each of a
plurality of supply containers. The liquids and powders received
therefrom are mixed in a mixing container, and a mixed liquid is
dispensed from the mixing container to a plurality of dispensing
containers. The system comprises flow rate regulators attached to
supply piping extending from the supply containers and dispensing
piping from the dispensing containers. A measuring device measures
the liquids or powders being supplied from the supply containers
and the mixed liquid being supplied from the mixing container to
the dispensing containers. The measuring device is installed on the
mixing container. A measurement control unit measures a flow rate
in each flow rate regulator under closed loop control by causing
the flow rate to change with the fuzzy logical inference in
proportion to each measured supply value and each measured
dispensing value. A moving unit moves the mixing container.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory diagram for a description of a liquid
measuring apparatus in one embodiment of this invention.
FIG. 2 is a block diagram for a description of a control process in
the apparatus shown in FIG. 1.
FIGS. 3(a) and 3(c) are graphical representations showing the
characteristic curves of flow control valves.
FIG. 3(b) is a graphical representation indicating the
characteristic curves of the flow control valve (a) of the
invention and of a conventional flow control valve (a').
FIG. 4 is a diagram for a description of the membership function of
fuzzy control.
FIG. 5 is a sectional side view of a flow control valve in the
invention.
FIGS. 6(a) and 6(b) are side views showing examples of the valve
head of the flow control valve in FIG. 5.
FIG. 7 is a graph for comparison of the results of metering in
which various types of flow control valves are used with the
embodiment of the invention of FIG. 1.
FIG. 8 is a flow sheet showing a second embodiment of a liquid
measuring system which can be a liquid and powder measurement
control method according to this invention.
FIG. 9 is a block diagram showing the control method of the
invention used with the apparatus of FIG. 8.
FIG. 10 is also a graphical representation showing the
characteristic curves plotted with the results of experiments which
have been performed according to the method of invention and the
conventional method.
FIG. 11 is a diagram of a two-liquid measured mixing apparatus as a
third embodiment of the present invention.
FIG. 12 is a control block diagram for explaining a multi-liquid
measured-mixing apparatus of FIG. 11 according to the present
invention.
FIG. 13 is a diagram of an apparatus which is a modification of the
apparatus of FIG. 11.
FIG. 15 is a flow chart of a liquid measured-mixing and
distributing apparatus as a fourth embodiment of the present
invention.
FIG. 16 is a block diagram of a control system used in the
embodiment of FIG. 15 of the present invention.
FIG. 17 is a graph of the measured deviation versus measuring time
and valve opening degree versus measuring time showing an example
of additive measuring according to the present invention.
FIG. 18 is a graph of metering deviation versus metering time and
valve opening degree versus metering time showing an example of
subtractive metering according to the present invention.
FIG. 19 is a flow chart of a conventional liquid metrically mixing
and distributing apparatus.
FIG. 20 is a flowsheet illustrating another liquid/powder
measuring-mixing-dispensing system.
FIG. 21 is a flowsheet illustrating a liquid/powder
metering-mixing-dispensing system of the fifth embodiment of the
present invention.
FIG. 22 is a block diagram of a closed loop control according to
the present invention applicable to the apparatus of FIG. 21.
FIGS. 23 through 26 are graphs used for an explanation of control
by fuzzy inference.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of this invention will be described with
reference to FIGS. 1-7.
FIG. 1 shows a liquid measuring apparatus employed in this
embodiment of the invention. It is operated according to a
subtraction type measurement method of observing the quantity of
liquid flowing out a measuring tank.
FIG. 1 illustrates a measurement control device 1. A load cell 2
measures the weight of raw material remaining in a measuring tank
8. A gravimeter amplifier 3 amplifies the signal from the load cell
2. A servo driver 4 is controlled by the measurement control device
1. A servomotor 5 is driven by the servo driver 4 to operate a flow
control valve 6 (to be described later). The flow control valve 6
adjusts the quantity of liquid flowing out of the measuring tank 8.
A stop valve 7 controlled by the measurement control device 1 stops
the outflow of liquid. The flow characteristic of the flow control
valve 6 is linear as shown in trace (c) of FIG. 3(a).
Now, a liquid measuring method according to the invention will be
described.
FIG. 2 shows a control process concerning the liquid measuring
method of the invention.
When a measurement target value is given to the measurement control
device 1, the control device calculates an initial valve opening
degree from the valve flow characteristic shown in FIG. 3 by fuzzy
inference. Fuzzy inference both for the initial setting and during
the successive measurement cycles will be described at the end of
this description. Upon the start of the measurement, the
measurement control device 1 applies an initial valve opening
setting through the servo driver 4 to the servomotor 5 of the flow
control valve 6, as a result of which the liquid flows out of the
measuring tank 8 and the actual weight value of the load cell 2
changes. On the other hand, an actual weight value outputted by the
gravimeter amplifier 3 is measured by the measurement control
device 1 with a predetermined control period. A fuzzy arithmetic
section 1--1 in the measurement control device 1 calculates a
difference between a measurement target value from the load cells
and an actual weight value and also calculates an amount of change
(with time) of the difference. It then calculates an observation
amount obtained by subjecting these data to low-pass filtering,
thereby to perform an inferential operation for a valve opening
degree according to a predetermined fuzzy rule. In this case, a
membership function for fuzzy inference is as shown FIG. 4 in which
the axis corresponding the above-described amounts of difference
between the measurement target value and the actual weight value
and the amount of change (with time) thereof, namely, physical
data, is divided such that the intervals for small physical data
are made fine. For instance, the axis is graduated
semi-logarithmically. This is to improve the measurement accuracy
and to reduce the measuring time. If the amount of difference is
large, a tight control characteristic is not always necessary, but
when the amount of difference is small, it is necessary to improve
the control accuracy. This is applicable to the primary filtering
function. In the case where the amount of difference is small, the
amount of difference of the primary filter is utilized to release
the dynamics of the measuring detector thereby to improve the
measurement accuracy.
FIG. 5 is a sectional side view showing one example of the flow
control valve employed in the invention.
As the servomotor 5 rotates, a feed screw 12 is rotated to move a
coupling board 13. A valve shaft 14 is secured to the coupling
board 13. Therefore, the valve shaft 14 and the coupling board 13
are moved vertically as one unit.
The term "servomotor" as used herein is not intended to be limiting
but may cover all electric motors such as an AC servomotor. DC
servomotor, and stepping motor (or pulse motor) which can control
mechanical positions, direction, angles and speeds (rpm).
A cylindrical or conical valve head 16 is formed on a
circular-truncated-cone-shaped valve face 15, which is tapered
towards the outlet of the flow control valve, in such a manner that
it is located inside a lower end portion 17 of a valve casing
(hereinafter referred to as "an outlet-side casing 17"). The valve
head 16 is so shaped that the rate of change of flow rate with
respect to a valve stroke H defined by the surface of the valve
head 16 and the valve seat 18 is small and linear as indicated by
the characteristic curve (c) in FIG. 3(a) or 3(c) or curve (a) of
FIG. 3(b).
The valve stroke 19 to fully open the valve is accommodated in an
upper end portion 20 of the valve casing (hereinafter referred to
as "an inlet-side casing 20". The servomotor 5 is used to move the
valve head 16.
Although the combination of the motor and the feed screw is
described herein as a method of moving the valve, other methods may
be used as long as an electrical signal is converted to a linear
movement. For example, an air servo cylinder may be used to move
the coupling board 13 directly.
The valve head 16 is conical as shown in FIG. 6(a) or cylindrical
as shown in FIG. 6(b). That is, it is so shaped that the rate of
change of flow rate with respect to valve stroke is small and
linear as shown in FIG. 3.
Each of the valve heads 16 shown in FIGS. 6(a) and 6(b) is so
formed that the relation of valve opening degree difference (h)
with valve opening area (a) is linear. Such a design rule may be
theoretically realized in the valve heads 16 of both FIGS. 6(a) and
6(b). However, they suffer practical difficulties.
Therefore, the valve heads shown in FIGS. 6(a) and 6(b) may be
formed with an approximate curve, or, in the case where the change
in area a per change in valve opening h can be held small, they may
be formed with one or more approximated straight lines.
When, in this case, the valve is substantially fully opened, the
linearity is liable to be lost. Therefore, in this case the range
of the linearity may be enlarged slightly more than the
theoretically necessary range by increasing the length of the valve
head and the diameter of the valve casing to thereby secure the
necessary range of linearity for the flow velocity. Also, the valve
casing may be made larger in diameter so that the valve is somewhat
large in dimensional margin so that the linearity can be obtained
over a larger range than required.
As was described above, the cylindrical or conical valve head is
formed on the circular-truncated-cone-shaped working face, which is
tapered towards the outlet of the valve, in such a manner that the
valve head is located inside the outlet-side casing. The valve head
is so shaped that, with respect to the valve opening degree defined
by the surface of the valve head and the valve seat, the rate of
change of flow rate with valve stroke is small and linear.
Therefore, with the flow control valve of the invention, the flow
rate can be finely controlled over the entire range of flow
rates.
Furthermore, the valve stroke to fully open the valve is provided
in the inlet-side casing. Therefore, when the fluid flows from the
inlet of the valve to the outlet, the resistance is low, and the
range of flow rates handled by the valve can be increased, for
instance, to 1:50.
Feedback control can be employed for the electric motor used to
operate the valve, and therefore the control resolution and
response characteristic can be improved as much.
In the present invention, any suitable material can be used for the
valve and valve casing. Preferably, the material and particularly
the hardness of the valve casing (including the inlet-side valve
casing, the outlet-side valve casing and the valve seat) may be
different from that of the valve (including the valve shaft and the
valve head) in order to increase the manufacturing accuracy and for
the purpose of preventing the valve casing and the valve from
biting each other because of impurities deposited thereon.
Preferably, the materials are suitably selected from the following
combinations: iron-stainless steel, stainless steel-stainless steel
(hard chrome plated), ceramic-stainless steel, and the like.
The terminology "electric motor" used in this specification means
such a motor in which the mechanical position, angle, revolution
number and the like can be controlled corresponding to an input
signal, for example and specifically, an AC servomotor, a DC
servomotor, a stepping motor (pulse motor), and the like.
In a closed loop liquid measuring method in which fuzzy control is
carried out, a motor-controlled flow control valve which is small
and linear in the rate of change of flow rate with valve stroke and
large in the maximum flow rate is employed according to the
invention.
Therefore, in the initial measuring period, the flow rate can be
high as in the case where the valve is fully opened and the
measuring speed can be correspondingly increased. Even when the
valve opening is decreased as the desired measurement value is
approached, the valve stroke can be greatly adjusted to control the
flow rate with high accuracy. Therefore, in the final measuring
period as well, the measuring speed is increased, the flow rate can
be controlled with high accuracy. Thus, when compared with the
fuzzy control with the conventional flow control valve, the fuzzy
control with the flow control valve of the invention can control
the flow rate quickly from the initial measuring period to the
final measuring period with high measurement accuracy.
SPECIFIC EXAMPLE 1
Three kinds of high-flow-rate flow control valves whose
characteristics are as indicated by curves (a), (b) and (c) in FIG.
3(a), respectively, were used to measure 1000 g of liquid. More
specifically the first (a) of the three flow control valves had a
characteristic substantially similar to that of a conventional
equal percent type flow control valve, the second (b) was a
conventional linear type flow control valve, and the third (c) was
a linear type flow control valve concerning the invention.
In the measurements with the three flow control valves, the fuzzy
control was employed. With the flow control valve (a), the
measurement was accomplished in sixty (60) seconds as indicated by
open rectangles in FIG. 7. With the flow control valve (b). the
measurement was achieved in fifty-one (51) seconds as indicated by
(X) in FIG. 7. With the flow control valve (c), the measurement was
accomplished in forty (40) seconds as indicated by (O) in FIG. 7.
With any one of the flow control valves, the measurement accuracy
was .+-.1.0 g or less. However, it was noted that the flow control
valve (c) was superior in measurement accuracy to the other two
flow control valves (a) and (b). It is true that the fuzzy control
is an excellent control method. However, it is apparent from the
above-described results of measurement that the measuring time
depends greatly on the flow control valve employed.
As is apparent from the above description, the effect of the flow
control valve is added to that of the fuzzy control, in the
invention.
That is, in addition to (1) the highly accurate measurement which
is free from disturbance, (2) the wide range measurement having a
wide range of measurement target values, and (3) the short time
measurement which does not depend on the measurement target value
(4) the quick measurement time and the excellent measurement
accuracy are obtained by the selection of the flow control
valve.
Accordingly, the measurement can be achieved in a much shorter time
in the liquid measuring method of the invention than in the fuzzy
control method using the conventional flow control valve. Thus, the
employment of the liquid measuring method of the invention will
greatly improve the efficiency of measuring work, and it will
contribute greatly to the rationalization of industry such as the
streamlining of measuring equipment.
Another and second preferred embodiment of this invention will be
described with reference to the accompanying drawings.
FIG. 8 is an explanatory diagram showing a liquid measuring
apparatus which is a key point of the invention, and is provided
with a powder measuring apparatus (not shown).
The liquid measuring apparatus will be described with respect to
the case where, as shown in FIG. 8, material filled in an upstream
tank 31 is conveyed to a downstream tank 32, which is a measuring
tank. The material is weighed with a load cell 34 coupled to the
downstream tank 32.
An FCV (flow control valve) 37 for varying the flow speed, a DRV
(drain valve) 39, an SPV (stop valve) 38, and a CDV (cleaning
drainage valve) 40 are provided in the pipe line between the
upstream and downstream tanks 31 and 32. The downstream tank 32 has
attached thereto the load cell 34 which is a detector for detecting
the weight of a material to be measured. The load cell 34 is
connected through a load cell amplifier 35 to a measurement control
device 33. The controller is connected to operating means, namely,
a servo driver 36 and the FCV (flow control valve) 37.
The liquid measuring apparatus thus organized performs the
measurement of the material to be measured as follows. The
measurement is started when a measurement target value is given to
the measurement control device 33 at the same time that the DRV
(drain valve) 39 and the CDV (cleaning drainage valve) 40 are
switched to stop draining the measurement line. When the
measurement control device 33 becomes ready for the measurement,
the SPV (stop valve) 38 is opened, and the measurement control
device 33 applies a position instruction to the servo drive 36 so
that the FCV (flow control valve) 37 is set to a predetermined
opening. That is, a servomotor 41 is driven to set the valve head
of the FCV 37 at the specified position, thereby to adjust the
opening degree. Thus, the raw material, namely, liquid is allowed
to flow from the upstream tank 31 to the downstream tank 32.
The load cell of the downstream tank 32 detects the weight of the
raw material thus moved into the tank, and feeds it back to the
measurement control device 33 through the load cell amplifier
35.
The measurement control device 33 calculates the difference between
the actual weight value and the target value, and the amount of
change (with time) of the difference. It calculates a valve opening
degree instruction (or position instruction) which provides a
suitable flow speed according to fuzzy control, learning control or
optimal control, so as to apply a new valve opening degree
instruction (or position instruction) to the FCV 37 to thereby
change the flow speed.
Thus, the opening degree of the FCV 37 is controlled in a closed
loop (FIG. 9) according to the data detected by the load cell 34 so
that it is approximated continuously or at predetermined time
intervals. When the measurement difference becomes small, the
opening degree of the FCV 7 is decreased, and accordingly the flow
degree of the FCV 7 is decreased, and accordingly the flow speed is
also decreased. Therefore, after suspension of the measurement, the
amount of residual inflow is small, and the measurement accuracy is
improved since it is not affected by the variation of flow speed
which may be caused by disturbance such as head differences in the
amount of liquid remaining in the upstream tank 31.
Although the method of controlling the opening degree of a valve is
described herein as a method of controlling a flow amount, a method
of controlling a pressure, in which a pressurizing means is
provided at a supply tank side, may be used.
In the measurement control device 33 of the invention, the control
of the FCV 37 depends on a measurement target value set for the
processing system at hand as long as it remains within the range of
measurement. Therefore, one and the same measuring apparatus can be
used for a variety of measuring target values. That is, the range
of measurement is increased as much as long as the static accuracy
of the detector is observed. Furthermore, during the measurement,
the operating pattern of the FCV 37 is changed. Therefore, for a
variety of measurement target values, the measurements can be
achieved substantially in one and the same short period of
time.
The liquid flow control valve in the invention is a
motor-controlled flow control valve (FCV) which is small and linear
in the rate of change of flow rate with valve stroke and large in
the maximum flow rate. One example of the flow control valve (FCV)
has been described with reference to FIGS. 3, 5, 6(a) and 6(b).
In the closed loop liquid and powder measurement control method of
the present invention, the difference between a freely determined
measurement target value and an actual measurement value are
outputted by a detector adapted to measure a material to be
measured.
The variations (with time) of the difference are utilized for fuzzy
control, learning control or optimal control of the liquid or
powder flow control means. Thereby, the motor-controlled flow
control valve which is small and linear in the rate of change of
flow rate with valve stroke and large in the maximum flow rate is
employed as the liquid flow control means. In the measurement
control method, and in the apparatus for practicing the method,
during the initial measurement period the valve opening is set to
be open wide to perform the measurement with high flow rate. Then
the valve is closed gradually with the lapse of time so that the
flow rate is controlled with high precision. Therefore, the range
of measurement is considerably wide, and the measurement time can
be reduced.
SPECIFIC EXAMPLE 2
FIG. 10 is a graphical representation for comparison of the
operation of one specific example of the apparatus of the second
embodiment of the invention with the operation of the conventional
apparatus using the conventional liquid flow control valve.
In the experiment, the detector capable of weighing 10 kg at
maximum was used, and the accuracy of the load cell was 1/5000. The
FCV (flow control valve) was position-controlled by the servomotor,
and the measurement control device outputted position
instructions.
FIG. 10 shows measurement characteristics provided when 1000 g was
measured by the conventional apparatus and the apparatus of the
invention which were equal in construction except for the liquid
flow control valves. In the graphical representation of FIG. 10,
measurement differences and FCV valve opening degrees are plotted
on the vertical axis, and the measurement time on the horizontal
axis. As is apparent from FIG. 10, in the case (marked with "0")
where the flow control valve (a) according to the invention was
used, the measurement was accomplished in thirty-one seconds on the
other hand, in the case (marked with triangles) where the
conventional flow control valve (a') was employed, the measurement
took forty-six (46) seconds. The measurement accuracy of the
conventional method was .+-.1.0 g, whereas that of the method of
the invention was .+-.0.5 g.
The closed loop liquid and powder measurement control method of the
invention performs fuzzy control, learning control or optical
control of the liquid and powder flow control means. In the
apparatus for practicing the method as is apparent from Japanese
Patent Application No. 106412/1987, the measurement can be carried
out with high accuracy over a wide range of measurement target
values without being affected by the variation of flow speed
attributed to disturbances. Also, the measurement can be
accomplished in a short time independently of the measurement
target value, with the result that the number of measuring devices
can be decreased and the raw materials can be economically used.
This system employs the above-described special flow control valve
according to the invention, whereby the measurement time is reduced
even more. Therefore, it goes without saying that the
above-described effects can be equally obtained, and moreover the
following effects are obtained according to the invention. The
initial cost and maintenance cost are reduced because the number of
measuring devices can be decreased as was described above. The
apparatus is high in reliability, that is, it rarely goes out of
order. Furthermore the amount of residual raw material is
decreased, and the running cost can be reduced as much.
A third embodiment of the present invention will be described with
reference to the drawings.
FIG. 11 shows an embodiment of the two-liquid measured mixing
system. This system is constructed so that raw-material liquids
from two tanks, which are supply tanks arranged on the upstream
side, are sent to one tank as a liquid receiving tank arranged on
the downstream side to thereby prepare a mixture liquid with
cumulative metering of the two liquids.
The two upstream tanks 71 and 72 are connected to piping paths 71a
and 72a to which are attached drain valves (DRVs) 69 and 77 and
stop valves (SPVs) 68 and 78. The DRVs 69 and 77 are provided with
special flow control valves (FCVs) 67 and 73 used in the present
invention.
As shown in FIG. 3(c), each of the flow control valves (FCVs) 67
and 73 has such flow-rate characteristic that the rate of change in
flow velocity is small and linear relative to the valve stroke.
Each of the flow control valves (FCVs) 67 and 73 has such a
structure as shown in FIGS. 5, 6(a) and 6(b).
Referring to FIG. 11, the piping paths 71a and 72a are connected to
a common coupling pipe 79. The coupling pipe 79 is provided with a
cleaning and disposal valve (CDV) 70 so that unadulterated liquid
can be transported to the downstream tank 62. A cleaning initiating
valve (CIV) 74 and an air duct valve (ADV) 75 are arranged on the
upstream side of the coupling pipe 79. The CIV 74 can introduce a
cleaning solution into the coupling pipe 79.
A load cell 64 is used as a detector for weighing the liquid and is
associated with the downstream tank 62. The load cell 64 is
connected to the measurement control unit 63 through a load cell
amplifier 65.
The measurement control unit 63 is connected to the switching unit
76 through a servo-driver 66 and performs fuzzy control on the
basis of the flow-rate characteristics of the FCVs 67 and 73, the
actual amount of the liquid measured by the load cell 64 and the
target value.
The switching unit 76 is connected to servomotors 67a and 73 for
actuating the FCVs 67 and 73 and to SPVs 68 and 78 arranged on the
two parallel liquid supply paths 71a and 72a, respectively.
Instructions to actuate the servo-driver 66 controlled by the
measurement control unit 63 are sent out from the switching unit 66
by which one of the two supplies is selected.
The operational process in the liquid measured mixing apparatus
thus constructed will be described with reference to FIG. 11 and
also to FIG. 12 which is a control block diagram.
Manufacturing conditions (conditions in measuring of the liquid of
the supply tank 71, the subsequent measuring of the liquid of the
supply tank 11, and the like) are specified to a measurement
control unit 63.
After measurement target values are established in the measurement
control unit 63. DRVs 69 and 77 and a CDV 70 are switched to a
measuring system line. When instructions to start measuring are
given, positional instructions are sent from the measurement
control unit 63 to a servo-driver 66 to open an SPV 68 and to open
a FCV 67 to a predetermined opening degree. The servo-driver 66
drives a servomotor 67a to set a valve port of the FCV 67 in an
instructed position thereby to adjust the opening degree to induce
a flow of the raw material. At that time, the initial opening
degree of the FCV 67 is calculated from the flow-rate
characteristic of the valve and the measurement target value by a
fuzzy control portion 302 (FIG. 12) of the measurement control unit
63 on the basis of fuzzy inference. As a result, transport of the
raw material from the tanks 71 to the receiving tank 62 starts. The
load cell 64 of the receiving tank 62 detects the weight of the
transported raw material and feeds the detected value back to the
measurement control unit 63 through the load cell amplifier 65.
A filter computing portion 301 of the measurement control unit 63
calculates the deviation between the measurement target value and
the fed back actual value and also the change in the deviation with
the passage of time. At the same time, it calculates values
produced by applying low-pass filter treatment thereto. The fuzzy
control portion 302 draws an inference from the calculated values
based on fuzzy rules, so that the opening degree of the valve to
produce suitable flow velocity in the next control cycle can be
found. In this condition, the membership function used the fuzzy
inference has the form as shown in FIG. 4, in which the axis
corresponding to the physical quantities of the deviation and the
change in deviation with the passage of time is divided into
semi-logarithmic intervals so that the portions corresponding to
small physical quantities are enlarged and a range of small
physical quantity is enlarged in the semi-logarithmic scale. This
achieves the double purpose of improving measuring accuracy and
shortening the measuring time. If the deviation is large, good
controllability is unnecessary, while if the deviation is small, it
is necessary to improve the controlling accuracy. This rule applies
to the temporal filtering function as follows. If the deviation is
small the deviation in the primary filter is used to relax the
dynamic characteristic of the measuring detector to thereby improve
the measuring accuracy.
When the measured deviation becomes small after initiation of
measuring, the opening degree of the FCV 67 is reduced to make the
flow velocity small. When the measured deviation and the change in
the measured deviation with time become so small that the measured
deviation is not larger than a predetermined value, the measuring
stops to close the SPV 68 and move the FCV 67 in the direction of
full close. In this condition the flow velocity is so small that
the quantity of residual inflow is also small. Accordingly,
immediately after the measuring stops, the quantity of inflow
becomes so small that measuring accuracy is improved independent of
the change of flow velocity. Further, the FCV 67 having the
flow-rate characteristic as represented by the curve c of FIG. 3(c)
depends on the fuzzy inferential calculation. Accordingly, more
accurate and more speedy measuring can be attained by the fuzzy
control method compared with the prior art method using
conventional flow control valves. Further, because the operation of
the FCV 67 changes within the measurement control range
corresponding to the measurement target value or the practical
system in the same manner as the fuzzy control using the
conventional flow control valve, the measuring can be made by one
and the same measuring unit regardless of the target value, so that
the measurement range can be enlarged within the static accuracy of
the detection end. Further, because the operational pattern of the
FCV 67 changes within the measuring time, the measuring can be made
for a predetermined short time regardless of the measurement target
value.
Next, the measuring of the liquid in the supply tank 72 is
selected. Another FCV 73 provided for the supply tank 72 is
selected by the switching unit 76. On the basis of the
predetermined measurement target value, the same measurement
control is made with measuring start instructions in the same
manner as described above. The control function in the control unit
is the same as described above, except that the output signal is
switched by the switching unit 76 to be sent to the FCV 73 and SPV
78 as operational terminals.
The liquid is transported to the receiving tank 62 through a
coupling pipe 79 which is common to all liquids from the supply
tanks. The inner diameter of the coupling pipe 79 is so large that
any residual part of the liquid in the pipe can drop naturally. To
improve the measuring accuracy, the piping length of the coupling
pipe 79 must be as short as possible. As an alternative method, the
supply tank 71 and 72 may be respectively and separately connected
to the receiving tank 62 without use of the coupling pipe. However,
the method has an disadvantage in equipment in that the piping is
complicated in construction when a plurality of liquids are
received, because the size of the mixer tank 62 is finite so that
the quantities of liquids to be mixed is limited. On the other
hand, the method is advantageous in higher accuracy measurements in
which the residual quantity within the coupling pipe 79 causes a
serious problem.
Although the case has been described in which the flow-rate
characteristic of the FCV 67 is equal to that of the FCV 73,
measuring can be done on the basis for values of different linear
characteristics with one and the same membership function and one
and the same set of fuzzy rules.
Accordingly, highly-accurate, wide-range and short-time measuring
can be attained regardless of the difference in the construction of
the system, the characteristics of the valves, and the like.
While an example of additive metering (in which the liquid reserved
in the mixer tank is measured) according to the present invention
has been described above, there are additionally provided DRVs 69
and 77, a CDV 70 a CIV (cleaning start valve) 74 and an ADV (air
duct valve) 75 which are attendant valves for cleaning, disposal
and the like.
When, for example, the measurement of the liquid in the supply tank
71, the cleaning, and the subsequent measuring of the liquid from
the supply tank 72 are carried out successively, the operation of
the aforementioned valves is as follows. When only the piping
should be cleaned after the measuring of the liquid from the first
supply tank 71, the CDV 70 is turned to the disposal side to open
the CIV 74 for the purpose of cleaning. At the same time, the ADV
75 and the SPVs 8 and 78 are closed. After the cleaning for a
predetermined time, the CIV 74 is closed and the ADV 75 is opened.
Then, the ADV 75 is closed for the next measurement of the liquid
from the second supply tank 72.
Although the aforementioned embodiment has shown the case where two
liquids are measured and mixed, it is to be understood that the
present invention is not limited to the specific embodiment and
that a large number of liquids may be measured in one and the same
liquid-receiving tank. It may be, however, most suitable for the
system that about eight flow control valves are controlled by one
and the same measurement control unit.
A modification of the present invention is described with reference
to FIG. 13.
This modification is constructed by a combination of an additive
measuring system in which the quantity of liquid is measured by a
detector associated with the liquid receiving tank, and a
subtractive measuring system in which the quantity of outflow
liquid is measured by a detector associated with the supply tank.
The description of the additive metering system will be omitted
because the embodiment of FIG. 13 has the same constituent parts as
those of the embodiment of FIG. 11 which are correspondingly
referenced.
In the drawing, the N-th supply tank 7N is provided with a load
cell 741 so that the tank serves as a measuring tank 7N.
The outflow quantity of the raw-material liquid from the tank 7N is
measured by the load cell 741 and, at the same time the liquid is
sent to the tank 62 acting as a liquid receiving tank and
cumulatively measured by the load cell 64. The actual values
obtained by the cumulative measuring system and the subtractive
measuring system are fed back to the measurement control portions
631 and 682 through the load cell amplifiers 65a and 65b,
respectively. The measurement control portions 631 and 682
calculate the deviations between the actual values and the
measurement target values and the changes in the deviations with
time and issue instructions to determine the opening degrees of the
valves on the basis of the set of fuzzy rules. The two output
signals of the measurement control portions 631 and 632 are
switched by a control-type switching unit 633 to control the
servo-driver 66.
According to the aforementioned construction, the measurement range
can be further widened by the subtractive measuring for performing
fine-scale measuring and the additive measuring for performing
large-scale measuring of a large set target value.
Further, in the system for producing only a solution, attendant
equipment, such as a stirrer, a warm-water circulator and the like,
may be provided on the measuring tank so that measuring, mixing,
reaction and the like can be carried out by one and the same
tank.
Although the aforementioned embodiment has shown the case where the
load cells are used as measuring detectors, the load cells may be
replaced by any other detectors. Examples of the detectors used
herein are pressure detectors, such as differential transmitters
and the like, various kinds of level meters, and the like. The
measurement range varies according to the static accuracy of the
used detector.
SPECIFIC EXAMPLE 3
In the following, the result of metering carried out by the
apparatus of FIG. 11 based on the aforementioned process is
shown.
The metering unit used in this example is capable of measuring up
to 10 kg. The accuracy of the load cell 64 is 1/5000. The FCVs
(flow control valves) are positioned by the servomotor on the basis
of positional instructions sent from the measurement control unit
63.
FIG. 3(c) shows the flow-rate characteristics of three kinds of
flow velocity control valves, in which curves a and b represent
conventional flow control valves, and a curve represents a specific
flow control valve according to the present invention. After the
valves were arranged in the system of FIG. 11, measuring was
carried out without change of the control system.
FIG. 14 shows the result of measuring up to 1000 g in the
aforementioned conditions.
Of course, the operational patterns of the opening degrees of the
flow control valves vary according to the kind of the valve. The
valve c according to the present invention terminated the
measurement in 40 seconds, whereas the conventional flow control
valves a and b terminated their measurement in 60 seconds and 51
seconds, respectively.
The effect was estimated by an experiment in which the same liquid
was used in the aforementioned system under the condition that the
flow control valves were established to be different in flow-rate
characteristic. Further, an experiment was conducted under the
condition that the quantities of liquids in the upstream tanks were
different. Consequently, highly-accurate, wide-range and short-time
metering could be attained by one and the same measurement control
unit and with the flow control valves according to the present
invention compared with the conventional flow control valves.
Further, in this measuring system, flow velocity varies according
to the residual quantity of the liquid in spite of the same opening
degree. However, the residual quantity of the liquid was measured
at each level, so that the measuring time and measuring accuracy
were satisfactory regardless of the different operational patterns
of the valve opening. On the other hand, with respect to the
measurement range, the accuracy of .+-.0.5 g in the range of 1:100
could be obtained.
As described above, according to the liquid metrically mixing
apparatus using fuzzy control and using the specific flow control
valves of the present invention, (1) reduction of the number of
measuring units can be reduced and (2) raw-material loss can be
reduced to a remarkable degree compared with the prior art, by use
of the measurement control unit which is not affected by the
measurement target values, residual liquid quantities and liquid
physical properties. Accordingly, a reduction of initial cost and a
reduction of the number of maintenance steps due to the reduction
in number of units can be attained. Further, reduction of running
cost due to the reduction of raw-material loss can be attained.
A fourth embodiment of the present invention will be described with
reference to FIG. 15.
Supply tanks 71 and 72 are filled with raw materials. A mixer tank
62 uses a load cell 64 as a detector. The liquid is finally
distributed to two distribution tanks 91 and 92. After two liquids
are measured a mixture thereof is distributed to downstream tanks
81 and 82.
Manufacturing conditions (conditions of measurement of the liquid
of the supply tank 71, succeeding measurement of the liquid of the
supply tank 72, and the like) are specified to a measurement
control unit 63.
After measurement target values are established in the measurement
control unit 63, drain valves (DRVs) 69 and 77 and a cleaning and
disposal valve (CDV) 70 are switched to the measuring-system line.
When instructions to start measuring are given positional
instructions are sent from the measurement control unit 63 to a
servo-driver 66 to open a stop valve (SPV) 68 and to open a flow
control valve (FCV) 67 to a predetermined opening degree. The
servo-driver 66 drives a servomotor to set a valve port of the FCV
67 in an instructed position to adjust the opening degree to induce
a flow of the raw material. As a result of this, transport of the
raw material from the supply tanks 71 to the mixer tank 62
starts.
The detector load cell 64 of the mixer tank 62 detects the weight
of the transported raw material and feeds the detected value back
to the measurement control unit 63 through a load cell amplifier
65.
The measurement control unit 63 computes a deviation between the
actual value and the target value as well as a change of the
deviation with the passage of time, etc. After computation, the
measurement control unit 63 issues opening instructions (positional
instructions) on the basis of a fuzzy control system to change the
flow velocity.
As described above, the opening degree of the FCV 67 is controlled
by a closed loop operating in a predetermined control cycle on the
basis of the value observed by the detector load cell 64, so that
the flow rate is controlled in a nearly continuously gradated
scale.
When the measured deviation becomes small, the opening degree of
the FCV 67 is reduced to make the flow velocity correspondingly
small. When the measured deviation and the change of the measured
deviation with time become so small that the measured deviation is
no larger than a predetermined value, the measuring stops by
closing the SPV 68 and moving the FCV 67 in the direction of full
close. In this condition, the flow velocity is so small that the
quantity of inflow is also very small. Accordingly, immediately
after the measuring stops, the quantity of inflow becomes so much
smaller that the measuring accuracy is improved independent of the
change of flow velocity. Further, because the operation of the FCV
67 changes within the measuring range corresponding to the
measurement target value or the specifics of the system, the
measurement can be made by one and the same measuring unit
regardless of the measurement target value, resulting in that the
metering range can be enlarged within the static accuracy of the
detection system. Further, because the operational pattern of the
FCV 67 changes within the measuring time, the measuring can be made
for a predetermined short time regardless of the measurement target
value.
Next, the measuring of the liquid in the supply tank 72 is
selected. Another FCV 73 which is provided to the supply tank 72 is
selected by the switching unit 76. On the basis of the
predetermined measurement target value, the same metrical control
is performed with measuring-start instructions in the same manner
as described above. The control function in the control unit 63 is
the same as described above, except that the output signal is
switched by the switching unit 76 to be sent to the FCV 73 and SPV
78 as operational terminals.
The liquid is thus transported to the mixer tank 62 through a
coupling pipe 79 which is common to all liquids from the supply
tanks. The inner diameter of the coupling pipe 79 is so large that
any residual part of the liquid in the pipe can drop naturally. To
improve measuring accuracy, the piping length of the coupling pipe
79 must be as short as possible. As another method, the supply
tanks 71 and 72 may be separately and respectively connected to the
mixer tank 62 without use of the coupling pipe 79. However, the
method has an equipmental disadvantage in that the piping is
complicated in construction when a plurality of liquids are
received, because the size of the mixer tank 62 is finite.
While an example of additive metering (in which the liquid reserved
in the mixer tank 62 is measured) has been described above,
additionally illustrated in the drawing are DRVs 69 and 77, CDV 70,
CIV (cleaning intake valve) 74 and ADV (air duct valve) 75 in the
drawing represent attendant valves for cleaning, disposal and the
like. When, for example, the measurement of the liquid in the
supply tank 71 is followed by cleaning and then by the measuring of
the liquid from the supply tank 72, the operation of the
aforementioned valves is as follows. When only the piping should be
cleaned after the metering of the liquid from the supply tank 71,
the CDV 70 is turned to the disposal side to open the CIV 74 for
the purpose of cleaning. At the same time, the ADV 75 and the SPVs
68 and 78 are closed. After the cleaning for a predetermined time,
the CIV 74 is closed and the ADV 75 is opened. Then, the ADV 75 is
closed for the next measurement of the liquid from the supply tank
72.
After the liquids from the supply tanks 71 and 72 are received, a
mixing process starts After mixing conditions are predetermined,
the mixed liquid is distributed to the downstream distribution
tanks 91 and 92 in the proportion of predetermined quantities. The
operational mode of the measurement control unit 63 is changed to
the subtractive measuring function and then the bottom step valve
of the mixer tank 62 is opened. As a result, FCVs 87 and 88 are
filled with the liquid to thereby change the weight of the mixer
tank 62. Accordingly, the measurement control unit 63 automatically
starts its subtractive metering function after the current weight
is reset to apparent zero just before the liquid will be
distributed to the downstream tanks 91 and 92. The subtractive
function is substantially the same as the additive function In
other words, the measuring operation is made to a distributed
quantity predetermined as a goal. In this embodiment, good
measuring accuracy is attained by operating the FCV 87 for the
measurement of the liquid and operating the FCV 88 for the
distribution of the residual quantity of the liquid.
FIG. 16 is a control block diagram.
In the present invention, the mixture measured in one mixer tank
may contain various kinds of liquids. It may be, however, most
suitable for the system that up to about either flow control valves
are controlled by one and the same measurement control unit.
Although the embodiment has shown the case where the coupling pipe
is used in the system, it is to be understood that the present
invention is not limited to the specific embodiment and that is
more highly accurate metering is required to solve the problem of
the residual quantity in the piping, the plurality of pipes may be
provided to be connected to respective liquid-receiving tanks.
Because the geometric arrangement of valves for distribution is as
shown in FIG. 15, the distance between the bottom valve of the
mixer tank and the respective flow control valve must be as short
as possible.
In the present invention, the load cell used as a detector for
measuring may be replaced by other detectors. Examples of the
detectors used herein are pressure detectors, such as differential
transmitters and the like, various kinds of level meters, and the
like. The metering range varies according to the static accuracy of
the used detector.
SPECIFIC EXAMPLE 4
An example in the system of FIG. 15 will be described.
The mixer tank 62 is capable of being measured up to 10 kg. The
accuracy of the detector load cell 64 is 1/5000. The FCVs (flow
control valves) 69, 73, 87 and 88 are positioned by the servomotor
on the basis of positional instructions sent from the metrical
control unit 63 when the liquids are metered, respectively.
FIG. 17 is a measurement time plot in the additive measuring
condition in which the liquid from the supply tank 71 is received.
FIG. 18 is a measurement time plot in the subtractive measuring
condition in which the mixed liquid is sent to the distribution
tank 91. In short the drawings show results in the case where the
measuring operation and the distributing operation were carried out
according to the same control system by one and the same
measurement control unit. Further the drawings show results in the
case where two kinds of liquids from the supply tanks 71 and 72
were measured respectively to be 1000 g and then 1000 g of the
mixture thereof was distributed to each of the distribution tanks
91 and 92.
Of course, the operational patterns of the opening degrees of the
FCVs 67 and 87 changed, but highly-accurate measuring and
distribution could be attained in a substantially equal time of
measuring.
The effect due to the difference in properties of the liquids was
estimated by an experiment in which the same liquid was used in the
above-described system under the condition that the flow control
valves 67 and 87 were established to be different in flow-rate
characteristic. Further an experiment was conducted under the
condition that the pressure heads in the upstream tanks were
changed suitably. Consequently, highly-accurate, wide-range and
short-time measuring and distribution could be attained by one and
the same measurement control unit and with only a modification of
the output portion thereof to be communicated with the flow control
valves.
According to the present invention, the liquid measured mixing
distributing apparatus cumulatively measures and mixes a plurality
of liquids to prepare a liquid mixture and for metrically
distributing the liquid mixture by closed-loop liquid measuring
means in which a velocity of flow is allowed to change
continuously. The apparatus comprises, a plurality of supply tanks
respectively filled with liquids as raw materials: a mixer tank for
mixing the liquids received from the supply tanks; a plurality of
distribution tanks to which the mixed liquid in the mixer tank is
distributed: a plurality of opening-regulated (flow-control) valves
respectively associated with the supply tanks and the distribution
tanks for restricting flow rates, each of flow-control vales having
a dead zone where no flow rate is generated within a predetermined
range: a detector arranged at the mixer for measuring liquids; a
measurement control unit for performing fuzzy control on the basis
of actual values measured by the detector and desiredly set target
values so as to calculate the opening degrees of the respective
flow-control valves; and a switching unit for switching the output
of the measurement control unit to a predetermined one of the
flow-control valves. Accordingly, the double function of a measured
mixing apparatus and a metrically distributing apparatus can be
attained by one and the same measurement control unit due to the
fuzzy control of one closed loop. Good metrical distribution can be
attained with highly-accurate, wide-range and short-time measuring,
so that simplification of equipment, increase of manufacturing
capacity and reduction of raw-material loss can be attained.
Accordingly, economic effects due to reduction of initial cost
maintenance cost and running cost can be attained.
A detailed description will now be given of the component elements
of the fifth embodiment of the present invention.
(1) Supply containers: containers for storing liquids or powders to
be measured. The capacity of the container should be at a scale fit
for production. The residual amount of stock material remaining in
the supply container is unrestricted. Theoretically the residue can
be measured down to zero. Moreover, any liquid or powder can be
measured down to zero as long as it has a physical property value
allowing it to flow out and which is unaffected by the physical
property value of the liquid or powder (e.g., viscosity, shape,
grain size, etc.).
(2) Flow rate regulators: There are provided as many flow rate
regulators as there are supply containers. In the case of liquids,
the flow rate regulator is an opening regulating (flow control)
valve and a flow velocity controller for changing the flow velocity
of the supply powder over a wide range by changing the opening of
the valve. A damper or screw feeder of a rotary type is suitable
for such a regulator for powders.
Moreover, each flow rate characteristic of the flow rate regulator
is such that no material flows out at about 0% of the rotation rate
or opening but allows a flow rate to occur at about 10% of the
maximum setting.
An AC servomotor, for instance, is employed to drive the flow rate
regulator.
For a shut-off valve for stopping the flow of the liquid and the
powder, a stop valve and a shutter gate are used respectively.
(3) Mixing container: a container having a capacity fit for the
production scale. Mixable liquids and powders are cumulatively
measured Provided that each of the transfer metering liquids or
powders is washed away, an unmixable liquid or powder may be
individually measured in the same container. In this case, they are
mixed by means of an agitator.
(4) Measuring device: There is provided one measuring device for
measuring the liquids and powders being supplied from the plurality
of supply containers as well as measuring the mixed liquid
dispensed from the mixing container.
The measuring device is installed on the mixing container side.
Cumulative measuring, either by addition or subtraction is possible
Use can be made of a tank measuring method by means of a load cell,
differential pressure transmitter, level meter or the like. There
are cases where the metering device is fitted to the mixing
container or mounted thereon.
(5) Measurement control unit. A measurement control unit changes
the flow velocity under closed loop control in such a manner that
it starts with processing a high flow rate, computes a deviation
from the measured value and a change of the deviation over time,
and changes the flow rate under closed loop control, i.e., fuzzy
control. Consequently, a wide range of metering is completed
accurately in a very short time. If the control unit is equipped
with a switching device, the plurality of liquids and powders and
the resulting mixed liquid can be measured cumulatively
(addition/subtraction) with one measuring device in one and the
same container. The number of supply containers adequately designed
therefor may be up to about eight, although the number can be
reduced.
(6) Switching device: A switching device is designed to control the
flow rate regulators for the plurality of supply containers and
dispensing containers with one drive control device and it forms
part of the measurement control unit. This arrangement makes it
unnecessary to fit a measurement control device and a drive control
device to each flow rate regulator.
(7) Moving unit. A moving unit conveys the mixing container. For a
conveying means, use can be made of an unmanned conveyer vehicle, a
conveyer or the like. In this case, the conveying function may be
attached to the mixing container or otherwise the mixing container
may be mounted on or dismounted from a separately provided moving
unit.
(8) Dispensing containers. Dispensing containers receive the
required amount of the mixed liquid and a suitable number of them
are installed, depending on the producing system.
The above-described component elements are the basic ones of the
present invention. The gist of the present invention is to arrange
these elements to perform the following steps, namely the steps of:
employing the measurement control unit for making the flow velocity
vaiable under closed loop control: having the metering control unit
perform the fuzzy control providing the moving unit for the mixing
container and effecting measured-mixing and measured-dispensing
with one measurement control unit.
Various attachment devices may be added for washing and other
purposes while the liquid and the powder are measured according to
the present invention. Spray balls for instance, are fitted to the
supply and dispensing containers and a switching valve is installed
in the middle of the piping. In addition warm water is circulated
from a constant temperature bath for heat insulation.
The liquid/powder measuring-mixing-dispensing system cumulatively
measures liquids and powders supplied from each of the plurality of
supply containers, mixes the liquids and powders received therefrom
in the mixing container, and dispenses the mixed liquid from the
mixing container to the plurality of dispensing containers
according to the present invention. The system comprises: (1) the
flow rate regulators attached to the supply piping extending from
the supply containers and the dispensing piping extending from the
dispensing containers; (2) the measuring device for metering the
liquids or powders being supplied from the supply containers and
the mixed liquid being supplied from the mixing container to the
dispensing containers, the measuring device being installed on the
mixing container side (3) the measurement control unit for
measuring a flow rate in each flow rate regulator under closed loop
control by causing the flow rate to change with the fuzzy logical
inference in proportion to each measured supply value and each
measured dispensing value; and (4) the moving unit for moving the
mixing container.
As a result first, since no coupling pipe is employed for the
supply pipe of the container for use in storing each supply liquid,
the facilities can be simplified. Secondly, the movable mixing
container (measuring tank or hopper) allows the reception of
liquids or powders from all of the supply containers and the
distribution of the liquids or powers thus measured to all of the
preparation tanks without fixed piping, whereby the size of the
mixing container can be reduced and it affords the flexibility of
the facilities. When versatile products are manufactured,
accordingly, idle facilities on the mixing container side can be
eliminated and further the addition of new facilities because of
the alteration of the formulation can be minimized. Thirdly, the
measuring cycle can be shortened by moving the mixing container, so
that temporal variations are minimized by large-scale preparation.
Fourthly, the mixing container (measuring tank or hopper) can be
used as a preparation tank by attaching an agitator to the mixing
container facing toward the supply tank. Fifthly, since the
measured-dispensing and the measured-mixing is performed under
fuzzy control using the same measurement control unit, it is
possible to improve the measuring accuracy, the measurement time is
shortened, loss of the mixed liquid is reduced and the facilities
are simplified.
Referring now to the accompanying drawings the fifth embodiment of
the present invention will be described in detail.
In this embodiment of the present invention, reference will be made
to a mixing container equipped with a measuring device and a moving
unit of a mobile type.
As shown in FIG. 21, it is assumed there are M sets of liquid
chemical supplying containers 102, N sets of powder chemical supply
containers 104 and L sets of dispensing containers 106. The
materials stored in the supply containers 102 and 104 are assumed
free from mutual contamination. Even though these are many formulas
for production, the total number of chemicals for use in each
formula for production is not more than N+M. In the conventional
production system, irrespective of being a moving or fixed type a
chemical supply container and a measuring device are required for
special use in each production formula in view of the measurement
range, measuring time and measuring accuracy, even if the formula
is the same. As a result, the number of sets exceeds M+N. However,
a measurement control unit for controlling the flow velocity in a
closed loop is employed and the measurement control unit is placed
under fuzzy control according to the present invention.
Accordingly, no consideration has to be given to the range of
measurement, the measurement time and the measuring accuracy, so
that M+N sets of supply containers are sufficient. Provided a
measuring device 108 is free from the contamination of liquid or
powder, the number of them may be set at an extremely small value
determined by the conveyance capability.
In this case, the installation of one mixing container 110 and one
metering device 108 (load cell) is assumed. At least M+N sets of
supply containers 102 and 104 are deemed sufficient, whereas the
number of mixing containers 110 equipped with the metering device
108 is determined in consideration of chemical preparation time and
the production scale of the formulation. Consequently, more than
one and not more than (M+N) sets of them may be required.
The measuring device is coupled to a measurement control unit 112
having a control block whose contents are shown in FIG. 22. The
output of the measurement control unit 112 is selectively applied
via the operation of a switching device 114 to a plurality M of
opening regulating valves 116 or N screw feeders and L opening
regulating valves 120 for the dispensing containers. More
specifically, a number of chemicals and liquids containing the
chemicals (M+N+L in total) are measured by the same control
algorithm in the same mixing container 110.
Flow rate regulators represented by the M opening regulating vales
116, the N screw feeders 118 and the L opening regulating valves
120 have flow rate characteristics, respectively as shown in trace
(a) of FIG. 3(c) or: i.e.. an equal percent characteristic for the
opening regulating valves 116 and 120 which are completely shut in
the proximity to the valve opening of 0%, whereas the outflow of
the liquid is started in the neighborhood of the valve opening of
about 10%.
The screw feeders 118 are capable of changing the powder feeding
flow velocity over a wide range as the number of its rotations is
varied.
The measurement control unit 112, including a filter computing
section 122 and a fuzzy control section 124 performs the fuzzy
control on the basis of the flow rate characteristics of the
opening regulating valves 116 and 120 and the screw feeders 118,
and also on the measured value and the set target value obtained
from the measuring device 108 in order to control the openings of
the opening regulating valves 116 and 120 and the number of
rotations of the screw feeders 118.
The operational process of the liquid/powder metering-mixing system
according to the present invention will now be described.
An instruction is given by a production control apparatus of a
higher level to the mobile mixing container 110 as to moving the
mixing container up to the position under the desired liquid or
powder supply container 102 or 104 (e.g. the second storage hopper
104).
Another instruction is given by the production control apparatus of
higher level via a coupling device as an attachment device of the
supply container 104 so as to couple a second coupling device 144
of the second supply container 104 and a coupling device 126 of the
mixing container 110 (metering tank). A further instruction is
given to the measuring device (load cell 108) for measuring the
powder chemicals being supplied from the second storage hopper 104
as the supply container. The switching device 114 as switched by a
system selection signal makes the floW rate regulator (screw feeder
118) of the second storage hopper 104 thus selected and a shut-off
valve (shutter gate 128) controllable by the measurement control
unit 112.
When preparation for measuring are confirmed through the initial
setting like this, an instruction for starting measuring is given
from the higher level. Under the instruction for starting
measuring, the switch device 114 is switched to select the supply
system initially selected, i.e., the powder supply system of the
second storage hopper 104 as set forth above and the second shutter
gate 128 is opened. A second driving motor 132 is driven and
rotated according to the instruction concerning the number of
rotations given by a drive control section 134 of the measurement
control unit 112 so that the screw feeder 118 transfers the powder
at the predetermined speed. The flow of the material is thus
started. The speed of the screw feeder 118 at that time is computed
in the fuzzy control section 124 of the measurement control unit
112 in conformity with the flow rate characteristics of the screw
feeder and the set measurement target value. The material in the
storage hopper 104 thus starts being transferred to the mixing
container 110. The measuring device 108 (load cell) of the mixing
container 110 detects the weight of the material transferred and
feeds back this value to the measurement control unit 112.
A deviation from the set target value and changes of the deviation
in terms of time are computed from the supply powder metering value
thus fed back in the filter computing section 122 of the
measurement control unit 112 and the quantity passed through a
low-pass filter is further computed therein. Inferential
computation based on the fuzzy rules is then carried out to produce
the speed of the screw feeder as an adequate flow velocity in the
following control cycle.
When the measured deviation is reduced after the commencement of
measuring, the number of rotations per unit time of the screw
feeder decreases to minimize the flow velocity. As the measured
deviation and the change of the measured deviation diminish, when
the measured deviation becomes less than a certain value, the
measurement is stopped and the shutter gate 128 moves toward the
completely shut position. The flow velocity at this time is lowest
and the inflow is very small. Consequently, the inflow after the
suspension of the measuring becomes small, whereas the measuring
accuracy improves without depending on the flow velocity
fluctuation. Moreover, the transition of the screw feeder 118
having the flow rate characteristic (a) of FIG. 3(c) allows for
about 10% leeway in the proximity to zero deviation in terms of the
number of rotations based on the fuzzy inference computation.
Accordingly, bad effects such as backlash are absorbed by means of
the dead zone and the fuzzy control, even though rotational
irregularities and mechanical backlash of the screw feeder are
present, and thus accurate measurement can be implemented. Further,
the operation of the flow rate regulator is changed by the set
measurement target value or processing system, so that the
measurement range is expanded because the same measuring device is
useable for measuring, irrespective of the size of the target
value. With respect to the measurement time, the operational
pattern of the flow rate regulator changes to make similar short
time measurements possible, irrespective of the size of the
measurement target value.
A description will now be given of the measuring of liquid intended
for mixture, for instance,
The mixing container 110 moves up to the position under the liquid
supply container 104 (e.g., the first tank 102) storing material
intended for mixture and simultaneously the switching device 114 is
switched to the first tank 102 so that the flow rate regulator
(opening regulating valve 152) and a first one of the shut-off
valves 130 are selected. The target value is preset and used for
control similar to what has been described above in accordance with
the measuring start instruction. In other words, the control
function in the control unit is the same and the output signal
applied to the screw feeder at the operational end and to the
shutter gate needs only to be switched by the switching device 114
to the proper opening regulating valve 152 and the shut-off valve
130.
The control signal applied by the measurement speed instruction
into a positional instruction corresponding to the opening before
being sent out. In other words, the output of the fuzzy control
section 124 is sent to a position conversing section 142 where it
is converted into a positional instruction signal before being
applied to the drive control section 154. The positional
instruction signal is used to drive a first one of drive motors 134
so as to set the first opening regulating valve 120 to the
specified position while regulating the opening. The flow of the
material is thus brought about. In this case, the initial opening
degree of the opening regulating valve 152 is computed in the fuzzy
control section 124 as in the case of the aforesaid powder metering
in such a manner that it is computed in accordance with the flow
rate characteristics of the valve 152 and the measurement value
based on fuzzy rules. The metering device 108 (load cell) attached
to the mixing container 110 detects the weight of the material
transferred and feeds back the value thus detected to the
measurement control unit 112.
The deviation from the target value and the change of the deviation
over time are computed from the measured supply liquid value thus
fed back to the fuzzy control section 124 of the metering control
unit 112 and the quantity passed through the low-pass filter 122 is
further computed therein. The inferential computation according to
the fuzzy rule is carried out in the fuzzy control section 124 on
the basis of the value thus computed so that an opening providing
an adequate flow velocity is obtained in the following cycle. In
this case, the flow rate characteristics of the valve 116 are such
that like those of the screw feeder 118, it is completely shut in
the proximity of 0% opening, whereas the liquid starts flowing out
in the proximity of about 10% opening. Based on the fuzzy
reasoning, the opening of the valve changes within a range of about
10%. As a result, the mechanical backlash of the valve is absorbed
so that accurate metering is implemented.
After the aforesaid operation is performed depending on the
contents thereof to measure and mix the whole chemical composition
within the range of formulas, it is dispensed to the downstream
containers.
The plurality of L dispensing containers 106 are connected to the
lower part of a pipe coupling device 136 in this embodiment. A
bottom valve 138 of the mixing container 110 (metering tank) is
controlled by a conveyance control device. When the bottom valve
138 is opened, the mixed liquid is dispensed though its coupler 140
to coupler 136 in an orderly process similar to what has been
employed for the flow rate regulators. In this case, the same
measurement control unit as shown in FIG. 22 is used to complete
the dispensing of the liquid accurately for a short time.
Although the mixing container 110 (measuring tank) is equipped with
the measuring device and the mobile moving unit, the measuring
device may be of a such a type that it is mounted on a measuring
table and used for measuring a predetermined position while being
conveyed by a unmanned conveyer
If the moving unit is of a mobile type, an electrical connecting
device such as a position sensor is required to be fitted to each
coupling position as an attachment device.
Although reference has been made to the load cell as a detecting
device for metering purposes, the same effect will be attained even
if a detector of any other tank metering type is employed. If a
differential pressure transmitter or the like is used for the
metering tank or hopper the mixing container can be anchored to the
mobile vehicle and therefore easily manufactured. It must be made
to be unaffected by vibration.
Precision metering in a wider range becomes possible if the
measurement control unit is provided with a subtractive measuring
function by fitting an additional measuring device to the supply
container (storage hopper or tank), in addition to the additive
measuring in the mixing container.
Although liquids and powders are received by one reception tank
(metering tank) and there measured in the present embodiment,
groups of liquids and powders may be dispensed separately to the
respective metering tank and hopper, respectively.
The liquid/powder measuring-mixing-dispensing system cumulatively
measures liquids and powders supplied from each of the plurality of
supply containers, mixes the liquids and powders received therefrom
in the mixing container, and dispenses the mixed liquid from the
mixing container to the plurality of dispensing containers
according to the present invention. The system comprises the flow
rate regulators attached to the supply piping extending from the
supply containers and the dispensing piping extending from the
dispensing containers, respectively. The measuring device measures
the liquids or powders being supplied from the supply containers
and the mixed liquid being supplied from the mixing container to
the dispensing containers. The measuring device is installed on the
mixing container side. The measurement control unit measures a flow
rate in each flow rate regulator under closed loop control by
causing the flow rate to change with the fuzzy logical reasoning in
proportion to each measured supply value and each measured
dispensing value. The moving unit moves the mixing container.
Accordingly, precision measurement can be performed unaffected by
flow velocity fluctuations due to disturbance and changes of
physical property values of substances being measured. The
measurement time can be shortened even over a wide measurement
range, whereas the measured-mixing and measured-dispensing can be
precisely and quickly implemented by one measurement control unit
with the least liquid loss. Therefore, it becomes possible to
simplify the production facilities reduce the number of measuring
devices and increase the production capacity even in the case of
large-scale facilities. At the same time, the improvement of
product quality and the reduction of material loss are accomplished
through large-scale preparation with the effects of initial cost
reduction, maintenance cost reduction, running cost reduction and
improvement of reliability.
Fuzzy inference will now be described. Fuzzy inference, used in a
fuzzy control system, is intended to emulate control by a human
operator. If the operator observes that the deviation between a
target value and a measured value is large and a time rate
variation of this deviation is small, then he would increase the
flow rate which decreases the deviation more quickly. On the other
hand, if he observes that the deviation is small but the time rate
variation is somewhat large, then he would slightly decrease the
flow rate. Fuzzy control is discussed by E.H. Mamdani in a
technical article entitled, "Application of Fuzzy Algorithms for
Control of a Simple Dynamic Plant" appearing in the Proceedings of
IEEE, Vol. 121, 1974 at pages 1585-1588 and by L.A. Zadeh in a
memorandum entitled, "Theory of Fuzzy Sets", Memo No. ERL-M502
Electronic Research Lab., University of California, Berkeley
(1975).
In FIG. 23 is plotted the deviation e (here the difference between
the target weight and the actual measured weight) as a function of
the time variation .delta.e (here the difference of the deviation e
between the present and the past measuring cycles). If the measured
deviation e and the measured time variation .delta.e fall within a
balance zone (enclosed by a dashed line). then the current flow
rate is appropriate in view of the current deviation so that the
valve opening or the like is not required to be changed. Rather
than performing an exact arithmetic computation, however, the
variables are designated by "vague" variables such as very small
small, medium large and very large. The "zero" balance zone may be
associated with the dead zone of the valve.
If the variables are designated by these vague variables and by
membership functions and if a control method is defined by
"if-then" rules, fuzzy measurement control becomes possible. A
fuzzy rule is generally expressed in the form of: if e is A and
.delta.e is B. then .delta.u is C. In the present invention, e is
the deviation, .delta.e is the time variation of the variation and
.delta.u is the time variation (between control cycles) of a
quantity controlling the flow such as the amount of opening of the
control valve. The variables A, B and C in the rules are likewise
defined by the vague variables, very small, small, etc.
The membership functions are defined for each of the deviation e,
the time variation of the deviation .delta.e and the time variation
of the control quantity .delta.u. Such a membership function for
the deviation e (in units of grams) is plotted in FIG. 24. The
vertical axis is the membership value a membership function varying
between 0 and 1. If the measured deviation is 3 gm, then the
deviation at the current measuring cycle is determined to be
"small". Similar membership functions must be created for .delta.e
and .delta.u.
For fuzzy control, a number of fuzzy rules are defined beforehand.
For example, a first rule is that if e is small and .delta.e is
large, then .delta.u is negative large; and a second rule is that
if e is small and .delta.e is medium, then .delta.u is negative
medium Other rules become apparent from FIG. 23. When each of e and
.delta.e falls in only one zone of the vague variables, then a
single fuzzy rule using those vague variables is used to obtain the
operation quantity .delta.u. If, however, the observed quantity
falls in two zones of vague variables two fuzzy rules for the
observed quantity must be used with the membership values acting as
weights in combining the "then" values of the operation quantities
.delta.u. For instance, FIG. 25 is a diagram used for obtaining the
control quantity .delta.u. Assume that e has a membership value 0.8
in the small zone, and .delta.e has a membership value 0.6 in the
large zone and value 0.7 in the medium zone. Further, providing
that fuzzy rules are (1) if e small and .delta.e is large, then
.delta.u is negative large and (2) if e is small and .delta.e is
medium, then .delta.u is negative medium. In this case, a
membership value of .delta.u is determined as the smaller one of
values of e and .delta.e (other selections are possible).
Accordingly, the membership value of .delta.u is 0.6 when rule (1)
is used, and 0.7 when rule (2) is used. From the membership values
.delta.u is obtained by calculating, for example, the center of
gravity of the area hatched in FIG. 25.
An initial opening degree of the valve is determined by a
membership function as shown in FIG. 26. For example, when the set
value is 1000 g, a membership value corresponding to the set value
is 0.5 from FIG. 2. The maximum opening degree of the valve is set
at 70.0 mm based on the flow-rate characteristics of the valve, so
that the initial opening degree of the valve is set at
70.0.times.0.5=35 mm. The fuzzy control is not initially conducted
for a while (wasted time). Since it takes a time to transfer the
liquid from a supply tank to a measurement tank, if the fuzzy
control is conducted immediately after initiating the measurement,
the opening degree of the valve may be increased excessively.
Accordingly, the fuzzy control is not conducted for the wasted
time, which is within 0-9.9 seconds.
In the measurement, fuzzy rules used are as follows:
(1) If deviation e is very large and its time variation .delta.e is
medium, then the time-variation of opening degree .delta.u is
positive medium,
(2) If e is very large and .delta.e is large, then .delta.u is
positive small,
(3) If e is very large and .delta.e is very large, then .delta.u is
zero,
(4) If e is large and .delta.e is very large, then .delta.u is
negative small,
(5) If e is medium and .delta.e is very large, then .delta.u is
negative medium,
(6) If e is medium and .delta.e is large, then .delta.u is negative
small,
(7) If e is large and .delta.e is large, then .delta.u is zero,
(8) If e is large and .delta.e is medium, then .delta.u is positive
small, and so on.
At point A in FIG. 23, fuzzy rule (1) is used so that .delta.u is
increased. At point A.sub.1 in FIG. 23, fuzzy rules (1) and (2) are
used so that the opening degree further increases. At point A.sub.2
in FIG. 23, fuzzy rule (2) is used. At point A.sub.3 in FIG. 23,
fuzzy rules (2) and (3) are used. At point B in FIG. 23, fuzzy rule
(3) is used so that the opening degree of the valve is not varied.
At point C in FIG. 23, fuzzy rules (3) and (4) are used so that the
opening degree of the valve is decreased. Between points C and D in
FIG. 23, some fuzzy rules are used as between points A and B. At
point D in FIG. 23, fuzzy rule (8) is used so that the opening
degree of the valve is increased.
* * * * *